As bearings disposed in, for example, gear boxes for wind-powered generation, medium-size roller bearings are often used. There are some cases where a windmill for use in wind-powered generation is placed in a non-steady operation which is other than a normal power-generating operation and in which rotary torque is not transmitted to a speed increaser, when electric power is cut off due to electricity outage or the like, when a control of reducing the rotary torque is performed due to high wind or the like, etc. In such a case, especially, a roller bearing mounted on a high-speed shaft rotates at a high speed in a nearly non-load state, so that a raceway surface of the bearing is not supplied with sufficient lubricant and therefore smearing (a phenomenon in which a plurality of minute seizures is generated) occurs on a raceway surface of a rotary ring or rolling contact surfaces of rollers, resulting in a reduced service life of the roller bearing.
Therefore, conventionally, in order to protect the raceway surface of the rotary ring and the rolling contact surfaces of the rollers, the raceway surface and the rolling contact surfaces are subjected to a surface treatment with manganese phosphate coating (see, for example, Patent Document 1).